Abstract Refrigeration for liquefying natural gas is provided by a closed cycle refrigeration system employing a multicomponent refrigerant. A stream of multicomponent refrigerant flowing in the closed refrigeration system is compressed and then successively fractionated by partial condensation in a plurality of steps to provide condensates at progressively decreasing temperature levels. The condensates are separated and introduced under reduced pressure into a common zone in heat exchange with the natural gas and vaporization of the condensates. A stream of multicomponent refrigerant including the resulting vapor from the condensates is withdrawn from the zone for recycle. The multicomponent refrigerant includes a mixture of components consisting essentially of nitrogen and a plurality of hydrocarbons. In one presently preferred variant, the refrigerant is a mixture of nitrogen and more than three hydrocarbons having molecular weights between the molecular weight of methane and the molecular weight of hexane. Two of the hydrocarbons are methane and ethane. Ethane is the component of greatest percentage, methane is the component of second greatest percentage, and nitrogen is present in a percentage substantially less than that of methane.
The method as claimed in claim 1 wherein the C2 hydrocarbon is present in an amount constituting at least 35 percent by volume of said multicomponent refrigerant.
Claim 2
Dependent Claim
23 words
The method as claimed in claim 1 wherein the average molecular weight of the multicomponent refrigerant is equal to or greater than 30.
Claim 3
Independent Claim
219 words
A system for liquefying a feed stream composed primarily of methane comprising: a. compressor means for compressing a multicomponent refrigerant comprising a plurality of hydrocarbons including a C2 hydrocarbon selected from the group of ethane and ethylene as the component of greatest percentage, and further including substantially more than 3 percent by volume of a nonhydrocarbon component having a normal boiling point substantially below that of methane, b. a plurAlity of heat exchange means and phase separator means connected in series for progressively condensing and separating said compressed multicomponent refrigerant into a plurality of liquid condensates and vapor portions decreasing temperatures, c. expansion means for expanding each of said liquid condensates, d. multistage heat exchanger means for vaporizing each of said expanded liquid condensates at the same vaporization pressure in each stage thereof, each of said heat exchanger stages including a shell portion and heat exchange passage means within each respective shell portion for passing one of said expanded liquid condensates in heat exchange relationship with both said feed stream and at least one of said vapor portions separated from said unexpanded condensate of said multicomponent refrigerant and undergoing condensation, and e. closed cycle means for withdrawing all of said vaporized condensates from said heat exchanger means and passing the same as said multicomponent refrigerant to said compressor means.
Claim 4
Dependent Claim
27 words
The system as claimed in claim 4 wherein the C2 hydrocarbon is present in an amount constituting at least 35 percent by volume of said multicomponent refrigerant.
Claim 5
Dependent Claim
23 words
The system as claimed in claim 4 wherein the average molecular weight of the multicomponent refrigerant is equal to or greater than 30.
Claim 6
Dependent Claim
34 words
The system as claimed in claim 4 wherein the combined percentage of the nonhydrocarbon component plus the C5 and heavier hydrocarbon components is greater than 11 percent but less than 21 percent by volume.
Claim 7
Dependent Claim
34 words
The method as claimed in claim 1 wherein the combined percentage of the nitrogen component plus the C5 and heavier hydrocarbon components is greater than 11 percent but less than 21 percent by volume.